"I wouldn't offer if I didn't think I could do it."
Bucky's attempt at stalling had already failed. Zemo had already moved away, pawing through the drawers and cabinets in search of the necessary items. "Believe it or not, your wellbeing is important to me, James. And if I thought myself incapable of stitching you up properly, I would find someone else to do it."
Once Zemo had collected everything he needed, he'd start wiping away the blood - as much as he could, since the injury was still actively bleeding - and sanitizing it. "I don't know how I'm going to do it," he spoke, tilting his head and leaning closer to Bucky's side, "But I'll figure out a way. I've killed them before, albeit while they were unconscious. But yes, I'm going back out there to kill them. Call it catharsis. You're also correct in the possibility of this leaving a scar --" Zemo briefly glanced up at Bucky, a mischievous smile on his face. "..and you're right about that too. Scars are sexy."
He spent a few more minutes cleaning the deep cut, trying to be as thorough as he could, then gestured towards the cot. "I'm sure this will be more comfortable for both of us if you sit."